/*===========================================================================*\
*                                                                           *
*                               OpenMesh                                    *
*      Copyright (C) 2001-2005 by Computer Graphics Group, RWTH Aachen      *
*                           www.openmesh.org                                *
*                                                                           *
*---------------------------------------------------------------------------* 
*                                                                           *
*                                License                                    *
*                                                                           *
*  This library is free software; you can redistribute it and/or modify it  *
*  under the terms of the GNU Library General Public License as published   *
*  by the Free Software Foundation, version 2.                              *
*                                                                           *
*  This library is distributed in the hope that it will be useful, but      *
*  WITHOUT ANY WARRANTY; without even the implied warranty of               *
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU        *
*  Library General Public License for more details.                         *
*                                                                           *
*  You should have received a copy of the GNU Library General Public        *
*  License along with this library; if not, write to the Free Software      *
*  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.                *
*                                                                           *
\*===========================================================================*/


//=============================================================================
//
//  Implements a simple singleton template
//
//=============================================================================


#ifndef __SINGLETON_HH__
#define __SINGLETON_HH__


//=== INCLUDES ================================================================

// OpenMesh
#include <Core/System/config.hh>

// STL
#include <stdexcept>
#include <iostream>


//== NAMESPACES ===============================================================


namespace OpenMesh {


	//=== IMPLEMENTATION ==========================================================


	/** A simple singleton template.
	Encapsulates an arbitrary class and enforces its uniqueness.
	*/

	template <typename T>
	class SingletonT
	{
	public:

		/** Singleton access function.
		Use this function to obtain a reference to the instance of the 
		encapsulated class. Note that this instance is unique and created
		on the first call to Instance().
		*/

		static T& Instance()
		{
			if (!pInstance__)
			{
				// check if singleton alive
				if (destroyed__)
				{
					OnDeadReference();
				}
				// first time request -> initialize
				else
				{
					Create();
				}
			}
			return *pInstance__;
		}


	private:

		// Disable constructors/assignment to enforce uniqueness
		SingletonT();
		SingletonT(const SingletonT&);
		SingletonT& operator=(const SingletonT&);

		// Create a new singleton and store its pointer
		static void Create()
		{
			static T theInstance;
			pInstance__ = &theInstance;
		}

		// Will be called if instance is accessed after its lifetime has expired
		static void OnDeadReference()
		{
			throw std::runtime_error("[Singelton error] - Dead reference detected!\n");
		}

		virtual ~SingletonT()
		{
			pInstance__ = 0;
			destroyed__ = true;
		}

		static T*     pInstance__;
		static bool   destroyed__;
	};



	//=============================================================================
} // namespace OpenMesh
//=============================================================================
#if defined(OM_INCLUDE_TEMPLATES) && !defined(OPENMESH_SINGLETON_C)
#  define OPENMESH_SINGLETON_TEMPLATES
#  include "SingletonT.cc"
#endif
//=============================================================================
#endif // __SINGLETON_HH__
//=============================================================================
